55. What is the difference between an extrinsic and an intrinsic factor?

An extrinsic factor is one outside of the population and influences it directly an example such as climate. A dry climate limits growth, a wet climate encourages growth.

The lemming pictured above shows a population increase on a three to five year cycle. The lemmings become very abundant, but before it becomes a catastrophic event, the lemmings die off. An intrinsic factor is built into the population itself, causes lemmings under the stress of high population numbers to lose the ability to produce sufficient amounts of insulin. (Another theory is that when the population gets large in the third or fourth year, the number of lemmings become very attractive to predators and that keeps the lemmings from becoming too abundant).